The invention relates generally to double or bi-directional overrunning clutch assemblies and more particularly to an actively controlled, bi-directional overrunning clutch assembly for use in motor vehicle driveline components such as transfer cases, transmissions, differentials and the like.
The sophistication of consumer vehicle four-wheel drive systems continues to increase. Initially, four-wheel drive systems were confined to trucks and vehicles primarily intended for off-road use. Such systems were both complex from a mechanical standpoint and complicated from an operational standpoint. Invariably, it was necessary to stop the vehicle to place the drive train into four-wheel drive and furthermore necessary to dismount the vehicle and manually activate drive hubs to couple the secondary drive wheels to the secondary axles.
Slowly the application of such systems expanded to light duty trucks, sport utility vehicles, vans and even some passenger cars as the systems became simplified, more sophisticated and easier to use. Such systems could often be activated on the fly and axle disconnects incorporated, for example, in the front differential obviated the need to dismount the vehicle to lock or unlock the manual wheel mounted locking hubs.
The current generation of four-wheel drive vehicles often includes adaptive drive systems wherein axle or wheel speed sensors provide data to a controller which selectively delivers torque or, contrariwise, applies braking, to control wheel slip, that is, front to rear speed differentials, in order to improve the driveability of such vehicles. The drivelines of such adaptive vehicle drive systems generally include a transfer case driven by the vehicle transmission which, through a modulating electromagnetic or hydraulically operated clutch, redistributes torque from the primary driveline and wheels to the secondary driveline and wheels. Typically, under conditions of no slip the primary driveline, which is coupled to and drives either the front or rear wheels of the vehicle, will carry and deliver substantially the full torque output of the transmission. When a speed differential is sensed, indicating wheel slip is present, the clutch increasingly couples the two drivelines, thereby transferring torque to the secondary driveline and wheels. When the modulating clutch is fully engaged, a fifty-fifty torque split exists between the primary and secondary drivelines.
Less complex four-wheel drive systems are also available. Typically such systems are full time rather than adaptive and include passive mechanical components such as viscous clutches or differentials having epicyclic gear trains which control torque delivery to the front and rear wheels of the vehicle. One early passive torque control configuration utilized a one-way or overrunning clutch to provide drive torque to the front wheels if the rear wheels should overspeed them, indicating that they were slipping. Such a passive, mechanical system was inexpensive but had the disadvantage of not operating in reverse gear. This disadvantage was overcome by the incorporation of double or bi-directional overrunning clutches which transfer torque to the secondary driveline in both forward and reverse gears while providing the desired torque transfer to the secondary drive wheels upon primary drive wheel overrun. However, passive mechanical double overrunning clutches do not always provide stable and predictable vehicle handling characteristics. Accordingly, improvement in the structure, operation and control of double overrunning clutch assemblies in motor vehicle drivelines is desirable.